easy wire sizing q

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j4str

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i belong to a powder coating message board, and most people build there own ovens. Some people are asking questions about what size wire to run. 12,400 watt oven and 75 foot run.



Ed,
Just verify that this all seems correct as my "code book" is just a cheap one based on the 2008 code. I am going to use 4- 3100 watt elements in a 4x4x8 oven. I have 75 feet from the electrical box so it looks like I am going to have to go down to a #4 wire and a 70 amp breaker.
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i think hes pretty well on the right track, but would you have to upsize because its a continuous load?
 
i don't think you can calculate it like a normal kitchen oven though. A kitchen oven they are counting on you not using all 4 burners while the top and bottom elements are turned on (clean mode)

When you turn on a big powder coating oven, it will always be drawing the full 12,400 watts
 
12.4kw running at 240v single phase will draw about 52 amps.
Being that it is used for powder coat it will probably run for 3hours and more at a crack?

If that's the case, and it were my barn, I'd go with a 60a breaker and the #4 wire.
I would probably also fuse each element individually. This makes things much easier when one breaks or is shorted. Further more if I did this I would step up to a 70a breaker on the feed.

My 2?
Doug S.

PS, if you are using a temp. controller it's not always pulling full load. AND depending on the controller it may cycle rapidly and almost constantly.
 
j4str said:
i don't think you can calculate it like a normal kitchen oven though. A kitchen oven they are counting on you not using all 4 burners while the top and bottom elements are turned on (clean mode)

When you turn on a big powder coating oven, it will always be drawing the full 12,400 watts
Click to expand...

No mention of service configuration... are we to assume they will be run on 240V???
 
Does this oven have any kind of thermostat to regulate the temperature or does it run on full power indefinitely?
 
im not sure if some of them have to controllers that let them run at half power or anything like that, thats a good question. Im pretty sure the one im gonna build will just have the thermostat controlling contactors, so the burners will simply be on or off.

or were you asking if they will be controlled by a thermostat or not. which they definitely are. Most big ovens get to temp in about 10-15 minutes
 
notice how the "easy wiring questions" become tough :D

since it's a message board and possibly covers many geographic areas, I think I should mention in TN you would be in trouble to start with the "build your own". In this state, equipment must bear a UL (or NRTL) label to be accepted.
That said, the critter seems to fit Art 422 Part II.
Restrictions there restrict open coil elements to a 50 amp overcurrent and resistive elements to no more than 48 amps on a 60 amp circuit.
From that, I would think you would be looking at at least two circuits.
It's a non-continus load and the 75 ft run shouldn't be much of a voltage drop issue. If I was the fellow with (4) 3100 watt elements, I;d supply it with (4) 20 amp circuits., with a 60 or 70 amp feeder for the total load.
Depending on the type wiring, you would be looking at a #6 cu minimum, probably #4 for the 70 amp..
There was no mention of a motor. If these are also equipped with a motor, then it's a different ball game.
 
if we just called this a 12,400 watt 240volt load. What would you need to supply it with?


12400 divided by 240 is 51.7 amps. If you were to call it continuous a 70 amp breaker would only be good for 56 amps at 80%. Therefor supply it with #4 and a 70 breaker. Is my logic off?
 
j4str said:
i don't think you can calculate it like a normal kitchen oven though. A kitchen oven they are counting on you not using all 4 burners while the top and bottom elements are turned on (clean mode)

When you turn on a big powder coating oven, it will always be drawing the full 12,400 watts
Click to expand...

Yeah, this isn't a range, I don't care where you come from.

Edit: Calculate it at max and feed it that way, cabadda bing cabadda boom.
 
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from what you said earlier, the load is not steadly on for 3 hrs so its; not continuous
51.7 amps #6
 
one other question, isn't there a table that says what gauge wire is good for what ampacity regardless of wire type. Like how if you look up #12 thhn, it says 25 amps, but if you look at the table im thinking of, it says #12 is only good for 20 amps, and overrides the other one

am i making any sense?
 
were it only that simple :smile:
In actuality one gage of wire of the same material will carry a given amount of amps and reach the same temperature. The complications come for the ambient temperature, type of insulation, enclosure (if any), ratings on terminations, etc.
For that reason there are many tables, stipulations and exceptions.
 
j4str said:
one other question, isn't there a table that says what gauge wire is good for what ampacity regardless of wire type. Like how if you look up #12 thhn, it says 25 amps, but if you look at the table im thinking of, it says #12 is only good for 20 amps, and overrides the other one
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That's "shall be protected at ..." and not "good for up to ..."

See 240.4(D)
 
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